build open-vmdk

This adds open-vmdk. This is a set of tools to create a stream-optimized vmdk, and an ova file from that. I will create a related PR with changes to make use of these tools to create a CoreOS ova file, which can be imported into VMware ESXi and Fusion/Workstation.

I don't know where to add this as adependency to the SDK, so that it gets built and installed in the SDK by default. Help is appreciated.